Wearable Broadband Circularly Polarized Antenna With Characteristic Mode Analysis for Wireless Body Area Network Applications

This letter presents a flexible, wearable, broadband circularly polarized antenna. A novel polarized conversion metasurface is loaded onto the flexible antenna, greatly expanding impedance and axial ratio bandwidths with the size of 52.6 mm × 49.6 mm × 6.325 mm (0.91λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.86λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.11λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 5.2 GHz). Besides, characteristic mode analysis is applied to reveal the working mechanism of the antenna. Experimental results indicate that an impedance bandwidth of 4.48 GHz to 8.39 GHz (60.8%) and a 3 dB axial ratio bandwidth of 4.43 GHz to 6.52 GHz (38.2%) could be achieved. Additionally, when the human tissue is 10 g, the peak specific absorption rate is 0.3800 W/kg, which is far below the limits of 2.0 W/kg under the 10 g average. The conducted robustness analysis demonstrates the antenna's exceptional stability under various operational conditions, making it a promising candidate for integration into wearable sensor systems.